Laser Wireless Power Transfer System With Active And Passive Safety Measures

ABSTRACT

A wireless laser power transfer system includes, in part, a transmitter and a receiver that form a wireless link. The transmitter, includes, in part, a first communication system, at least a first source of laser beam, and a controller adapted to vary power and direction of the laser beam and further to modulate the laser beam. The receiver includes, in part, a communication system adapted to establish a wireless link with the first communication system, at least a first photo-voltaic cell, and a controller adapted to demodulate and detect the power of the modulated laser beam received by the first photo-voltaic cell from the first source of laser beam. The system optionally includes at least a second source of laser beam controlled by the transmitter controller. The system optionally further includes a second photo-voltaic cell. The transmitter controller is further adapted to cause the second laser beam to strike the second photo-voltaic cell.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims benefit under 35 USC 119(e) ofApplication Ser. No. 62/340,951, filed May 24, 2016, the contents ofwhich is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to wireless power transfer, particularlyusing lasers.

BACKGROUND OF THE INVENTION

Wireless power delivery has been an active field of research. NASA hasbeen working on systems to use high intensity lasers to power small UAVsor Vehicles. Due to laser safety regulations, however, such systems havea limited power delivery capability. While high intensity laser are usedin the industry, their use is restricted in closed environments wherepeople are not present. Laser radiation injury is mainly caused bythermal damage to the living tissue.

While laser skin burns only happen under extremely powerful laser beams,human retina is quite sensitive and can damage under much lowerintensities. The IEC60825 is an international standard that specifiesthe limits and classes of lasers. Based on the IEC60825 standard, themaximum permissible exposure (MPE) at the human cornea depends on boththe laser energy and duration of exposure. FIG. 1 shows a plot of MPEfor different wavelengths at different exposure times, and assuming thatthe power is concentrated directly at the cornea.

BRIEF SUMMARY OF THE INVENTION

A wireless laser power transfer system, in accordance with oneembodiment of the present invention includes, in part, a transmitter anda receiver that form a wireless link. The transmitter, includes, inpart, a first transceiver, at least a first source of laser beam, and afirst controller adapted to vary a power and a direction of the laserbeam and further to modulate the laser beam. The receiver includes, inpart, a second transceiver adapted to establish a wireless link with thefirst transceiver, at least a first photo-voltaic cell, and a secondcontroller adapted to demodulate and detect the power of the modulatedlaser beam received by the first photo-voltaic cell from the firstsource of laser beam.

In one embodiment, the transmitter further includes, in part, at least asecond source of laser beam. The first controller is further adapted tovary a power and a direction of the second laser beam, and further tomodulate the second laser beam. In one embodiment, the first controllermodulates the first and second laser beams using the same modulationtechnique. In one embodiment, the receiver further includes, in part, asecond photo-voltaic cell. The controller is further adapted to causethe second laser beam to strike the second photo-voltaic cell.

In one embodiment, the first controller is further adapted to cause thefirst laser source to operate at a first power level if the power of thelaser beam received at the receiver matches an expected power level. Inone embodiment, the first controller is further adapted to cause thefirst laser source to operate at a second power level if the power ofthe laser beam received at the receiver does not match the expectedpower level, said second power-level being either zero or an eye-safepower level.

In one embodiment, the first controller causes the first laser source tooperate at the first or second power level in response to data the firstcontroller receives from the second controller. The data is exchangedbetween the first and second transceivers. In one embodiment, the firstlaser source is disposed on a first panel and the second laser source isdisposed on a second panel. The first and second panels are positionedat different orientations with respect to the first photo-volatile cell.In one embodiment, the laser has a bandwidth ranging from 250 nm to 450nm.

A method of transferring laser power wirelessly, in accordance with oneembodiment of the present invention includes, in part, setting the powerof at least a first laser beam to a first value, modulating the firstlaser beam, delivering the first laser beam to at least a firstphoto-voltaic cell, demodulating the delivered laser beam, detecting thepower of the delivered laser beam, and varying the power of the firstlaser beam to a second value greater than the first value if thedetected power value matches an expected power.

The method, in accordance with one embodiment of the present inventionfurther includes, in part, generating at least a second laser beam,modulating the second laser beam, and varying the power and thedirection of the second laser beam. In one embodiment, the first andsecond laser beams are modulated using the same modulation technique. Inone embodiment, the method further includes, in part, disposing a secondphoto-voltaic cell adjacent first photo-voltaic cell. In one embodiment,the method further includes, in part, causing the second laser beam tostrike the second photo-voltaic cell.

In one embodiment, the method further includes, in part, changing thepower of the first laser beam from the second value to the first valueif the detected power value does not match the expected power value. Inone embodiment, the method further includes, in part, changing the powerof the first laser beam from the first value to the second valuefollowing the change from the second value to the first value if thepower value is detected to match the expected power value following anexpiration of a first time period.

In one embodiment, the method further includes, in part, causing thepower of the first laser beam to change from the first value to thesecond value, and from the second value to the first value in responseto data exchanged wirelessly between a first controller controlling thefirst laser beam and a second controller responsive to the firstphoto-voltaic cell. In one embodiment, the first laser source isdisposed on a first panel and the second laser source is disposed on asecond panel. The first and second panels are positioned at orientationswith respect to the first photo-volatile cell. In one embodiment, thelaser beam has a bandwidth ranging from 250 nm to 450 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of MPE for different wavelengths at different exposuretimes, as known in the prior art.

FIG. 2 is a simplified high-level block diagram of a wireless laserpower transfer system, in accordance with one exemplary embodiment ofthe present invention

FIG. 3 is a simplified high-level block diagram of a wireless laserpower transfer system, in accordance with another exemplary embodimentof the present invention.

FIG. 4 is a simplified high-level block diagram of a wireless laserpower transfer system, in accordance with another exemplary embodimentof the present invention.

FIG. 5 is a simplified high-level block diagram of a wireless laserpower transfer system, in accordance with another exemplary embodimentof the present invention.

FIG. 6 is a simplified high-level block diagram of a wireless laserpower transfer system, in accordance with another exemplary embodimentof the present invention

FIG. 7 is a flowchart for safe transfer of laser power wirelessly, inaccordance with one embodiment of the present invention.

FIG. 8 is a flowchart for safe transfer of laser power wirelessly, inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with embodiments of the present invention, one or morehigh power laser beams are transferred wirelessly to power a devicewhile satisfying the MPE safety standards. Embodiments of the presentinvention include active and passive protective techniques to provide ascalable solution for a selected level of wireless power deliverywithout surpassing the MPE safety levels. The active protection/safetysystems ensure that the exposure time never exceeds a predefined value(10 us for example). The passive protection/safety systems reduce thebeam power intensity (power per unit area) by increasing the effectivebeam width.

FIG. 2 is a simplified high-level block diagram of a wireless laserpower transfer system 100 with active safety protection, in accordancewith one exemplary embodiment of the present invention. System 100 isshown as including, in part a laser beam transmitter (alternativelyreferred to herein as transmitter) 110, and a laser beam receiver(alternatively referred to herein as receiver) 150. Transmitter 110includes at least one laser beam generator and scanner (collectivelyreferred to herein as laser scanner or scanner) 114, a controller 112and a wireless communication system 116. The scanner may be a galvoscanner, MEMS micro-mirror scanner, accousto optic scanner, an opticalphased array, or the like. Receiver 150 includes one or morephoto-voltaic (PV) cells 154, a controller 152, and a wirelesscommunication system 156. Each of communication systems 116, 156 may bea transmitting unit, a receiving unit or a transceiver. The followingdescription of the embodiments of the present invention are providedwith reference to the communication systems being transceivers. However,it is understood that the above embodiments of the present invention arenot so limited and other communication systems such as transmittingunits or receiving units may also be used. Transmitter 110 and receiver150 are adapted to communicate with one another using a wireless link(e.g., infrared or RF) established between their respectivetransceivers. It is understood that the drawings do not show antennasthat may be used in some embodiments, such as those that use RF signalsfor wireless transfer of information.

Controller 112 is adapted to control laser beam scanner 114 to directlaser beam emitted from the laser source to PV 154. Controller 112 isfurther adapted to control and vary the power of the laser beamgenerated by scanner 114. Accordingly the laser beam may have an outputlevel that is eye-safe for any duration of exposure, as well as amultitude of higher power levels for delivery to receiver 150. In oneembodiment (not shown), the laser beam generated by scanner 114 mayinclude a fiber optic assembly having disposed therein a centrallaser/optical source distributing the optical power via the fiber opticassembly. Such a central source may receive its energy from electricityor directly from sunlight (e.g., solar pumped lasers). The laser beamreceived by PV 154 is converted to electrical energy by PV 154 and usedto charge device 180.

The laser beam emitted by transmitter 110 is modulated by controller 112to have a unique signature associated with scanner 114. In oneembodiment, such a signature is defined by a frequency modulationtechnique used to modulate the transmitted laser beam. After the laserbeam arrives at the PV cell, a corresponding frequency demodulationtechnique is used on the output current of the PV cell(s) to identifythe signal and determine whether it has the expected signature. Inanother embodiment, such a signature is defined by an amplitudemodulation technique used to modulate the amplitude of the transmittedlaser beam. In yet other embodiments, the beam may be encrypted oraltered to include a unique signature.

Controller 152 is adapted to use a corresponding demodulation techniqueon the output current of the PV cell(s) to identify the signal anddetermine whether it has the signature with which the signal wasmodulated—referred to herein as the expected signature at the receiver.In one embodiment, as long as the laser power received by receiver 150is detected as matching the power of the laser beam transmitted bytransmitter 110, and is identified to have the expected signature,controller 152 continues to transmit a clear-to-send signal viatransceiver 152 to transmitter 110. In response to receiving theclear-to-send signal, controller 112 causes scanner 114 to transmit thelaser beam to receiver 150.

The power of laser beam 125 stays low to and in an eye-safe power level,or is otherwise reduced to zero as described further below, as long asthe laser beam is not targeted on the PV cell(s), or is not identifiedby the PV cells as having the expected signature, or if the path betweenthe transmitter and receiver is not detected as being clear, therebycausing a reduction of the laser power at the receiver. As long as theseconditions are met, the receiver sends a clear-to-send signal to thetransmitter. Once the clear-to-send signal is received from thereceiver, the transmitter increases the laser power for wireless powerdelivery. If any of these conditions are not met, the clear-to-sendsignal is aborted thus causing controller 112 to shut off the laser orreduce the laser power to an eye-safe power level.

If an object stands in the path of and blocks the laser beam fromdirectly reaching PV cell 154, the power level of the laser beamtransmitted by scanner 114 and possibly reflected/scattered off objectsand subsequently received by PV cell 154 is detected to be less than thepower level of the transmitted beam. Accordingly, even though such areflected/scattered beam is identified by controller 152 as having theexpected signature, because its power level is detected as being lessthan that of the transmitted beam, transmitter 110 stops transmittingthe clear-to-send signal, thus causing controller 112 to stoptransmitting the laser beam via scanner 114. Accordingly, anymechanical/physical movement that blocks the path of the laser beam fromthe scanner 114 to PV cell 154 is detected quickly (e.g., within a fewmicro seconds) thus causing the transmission of the laser beam to end.In other words, because the presence of, e.g., a person or a pet movingin the path of the laser beam is quickly detected, any possible damageto the skin or cornea that would otherwise result from the beam issubstantially mitigated and thus prevented.

A laser beam received by PV cell 154 and detected by controller 152 ashaving the power level but not the signature of the transmitted beam,causes controller 152 to stop transmitting the clear-to-send signal,thereby causing transmitter 110 to stop transmitting the laser beam.Accordingly, the transfer of the laser power continues to occur at ahigh level as long as both the power and the signature of thetransmitted beam matches the power and signature of the beam as expectedat the receiver.

Assuming a maximum shut-down delay of to and a corresponding MPE of W₀,the maximum allowable continuous power of the laser satisfying thesafety regulation requirement may be defined as following:

$P_{{laser},\max} = \frac{W_{0}}{t_{0^{\prime}}}$

For example, for a laser with wavelength of 800 nm and beam width of 1cm², if to is 100 μsec, from FIG. 1, it is seen that W₀=3 e⁻⁶ J/cm2,corresponding to a laser power of P=30 mW. If to is reduced to 1 μsec,then the laser power may be as high as 1 W. The maximum allowable laserpower satisfying the safety regulation calculated above is for one beamof laser. By aggregating the power from multiple beams highertransmitted wireless power levels can be achieved without violating thesafety regulations.

FIG. 3 is a simplified high-level block diagram of a wireless laserpower transfer system 200 with active safety protection, in accordancewith another exemplary embodiment of the present invention. System 200is similar to system 100 except that system 200 is shows as includingmore laser sources than PV cells. The exemplary embodiment of FIG. 3 isshown as including, in part, 3 laser sources, namely 120 ₁, 120 ₂ and120 ₃, and 1 PV cell 154. Scanner 114 is adapted to control and scan thedirection of the beams 125 ₁, 125 ₂, 125 ₃ supplied respectively bysources 120 ₁, 120 ₂, 120 ₃ so as to ensure that these beams strike PVcell 154 as long as transceiver 116 receives a clear-to-send signal fromtransceiver 156.

Each of laser sources 120 ₁, 120 ₂ and 120 ₃ has a unique signature thatcontroller 152 is adapted to identify. The signatures may bepre-programmed in controller 152 or be transmitted to controller 152using the wireless link established between transmitter 110 and receiver150 via their respective transceivers 116 and 156. The wireless link,which may be an RF link, an infrared link, or the like enablesindividual transmitter and receivers to be identified in a network ofsuch devices.

Assume that the electrical signal generated by PV cell 154 has severaldifferent components representative of the laser beams it received.Controller 152 is adapted to perform, for example, a Fast Fouriertransform on the output signal of PV cell 154 to identify the signatureof such components. If the signatures so identified match the signaturesof the beams, and the power level of the beams match their expectedpower levels, a clear-to-send signal is transmitted by receiver 150 totransmitter 110 to enable sources 120 ₁, 120 ₂, 120 ₃ to continue totransmit. Assume, for example, that controller 152 is able to identifyonly the two signatures associated with beams 125 ₁, 125 ₃. Accordingly,the clear-to-send signal includes information directing transmitter 110to continue to transmit from laser sources 120 ₁, 120 ₃ and shut offtransmission from source 120 ₂. As described above, if, for example, thesignature of all three beams is present in the electrical signalreceived by PV cell 154 but the power level associated with any of thebeams (e.g., beam 125 ₁) falls below the beam's expected power level atreceiver 150 (due, for example to partial or full obstruction of thebeam), the clear-to-send signal includes information directingtransmitter 110 to shut off the laser source whose power level at thereceiver is detected to have fallen below the expected level or reduceits power to an eye-safe level (e.g., source 120 ₁).

FIG. 4 is a simplified high-level block diagram of a wireless laserpower transfer system 300 with active safety protection, in accordancewith another exemplary embodiment of the present invention. System 300is similar to system 100 except that system 400 is shows as includingmore PV cells than laser sources. The exemplary embodiment of FIG. 3 isshown as including, in part, three PV cells 154 ₁, 154 ₂ and 154 ₃, andone laser source 120. Scanner 114 is adapted to control and scan thedirection of the beams 125 supplied by laser source 120 so as to ensurethat beam 125 strikes at least one of the PV cell 154 ₁, 154 ₂ in anunobstructed manner.

Laser source 120 has a unique signature that controller 152 is adaptedto identify. The signature may be pre-programmed in controller 152 or betransmitted to controller 152 via the wireless link established betweentransmitter 110 and receiver 150 through their respective transceivers116 and 156.

Assume that after calibration and scanning, receiver 150 issues aclear-to-send signal to transmitter 110 thereby causing laser source 120to strike, e.g., PV cell 154 ₂. The emission of beam 125 on PV cell 154₂ continues so long as both the power and the signature of beam 125matches the power and signature of this beam as expected at thereceiver. If an object blocks the path of beam 125, thereby causing thereceived laser power to no longer match the expected power at thereceiver, the clear-to-send signal is aborted, thereby causingcontroller 112 to shut off or reduce the power of laser source 120 to aneye-safe level. In some embodiments, if the duration of such shut-offperiod extents a pre-defined threshold value, controller 112 causesscanner 114 to change the direction of beam 125 so as to cause beam 125to strike another PV cell, such as PV cell 154 ₁. In other words, inaccordance with such embodiments, if the path of the laser beam to oneor more of the PV cells is detected to have been blocked, the lasersource may continue to charge device 180 via another unobstructed PVcell.

FIG. 5 is a simplified high-level block diagram of a wireless laserpower transfer system 400 with active safety protection, in accordancewith another exemplary embodiment of the present invention. System 400is similar to system 100 except that system 400 is shown as including amultitude of laser sources and a multitude of PV cells. The exemplaryembodiment of FIG. 5 is shown as including, in part, three PV cells 154₁, 154 ₂, 154 ₃, and three laser sources 120 ₁, 120 ₂, and 120 ₃. It isunderstood, however, that a wireless laser power transfer system, inaccordance with embodiments of the present invention, may have anynumber M of laser sources, and any number N of PV cells, where M and Nare integers that may or may not be equal.

Scanner 114 is adapted to control the laser sources so that beams 125 ₁,125 ₂ and 125 ₃ emitted respectively by laser sources 120 ₁, 120 ₂ and120 ₃ strike PV cells 154 ₁, 154 ₂, and 154 ₃ to avoid crossing of thebeams. Controller 154 is adapted to identify and validate the signatureassociated with each beams 125 ₁, 125 ₂ and 125 ₃. If all three beamsare safely on, i.e., none has been shut off or has its power reduced toan eye-safe level for safety reasons in accordance with embodiments ofthe present invention, then beam 125 ₁ is recognized as a valid beamwhen received at PV cell 154 ₁, beam 125 ₂ is recognized as a valid beamwhen received at PV cell 154 ₂, and beam 125 ₃ is recognized as a validbeam when received at PV cell 154 ₃; accordingly, a clear-to-send signaltransmitted by receiver 156 may include information specific to each oflaser sources 120 ₁, 120 ₂ and 120 ₃.

Assume, for example, that as a result of the movement of an object(e.g., a person), the path from source 125 ₂ to PV cell 154 ₂ is fullyor partially blocked. Accordingly, controller 152 instructs controller112 to no longer transmit beam 125 ₂ to PV cell 154 ₂. Upon receipt ofsuch an instruction, controller 112 may shut off laser 120 ₂ oralternatively lower the power of laser 120 ₂ to an eye-safe level andthereafter cause scanner 114 to steer beam 125 ₂ until beam 125 ₂strikes any of the other two adjacent PV cell 154 ₁ or 154 ₃. Controller152 is thus configurable to recognize the signature of a beam (e.g.,beam 125 ₂) when received at another PV cell (e.g., 154 ₁) when theoptical path between the source of the beam (e.g., beam 125 ₂) and theprimary PV cell (e.g., 154 ₂) assigned to that beam is fully orpartially blocked. After validating the signature and power of beam 125₂ at cell 154 ₂, transmitter is instructed via the wireless link toraise the power of the beam 125 ₂ to a higher value.

Similarly, assume, for example, that as a result of an object movement,the path from source 125 ₃ to PV cell 154 ₃ is fully or partiallyblocked. Accordingly, controller 152 instructs controller 112 to nolonger transmit beam 125 ₃ to PV cell 154 ₃. Upon receipt of such aninstruction, controller 112 may shut off laser 120 ₃, or alternativelylower the power of laser 120 ₂ to an eye-safe level, and thereaftercause scanner 114 to steer beam 125 ₃ until beam 125 ₃ strikes PV cell154 ₂. Controller 152 is thus configurable to recognize the signature ofa beam (e.g., beam 125 ₃) when received at another PV cell (e.g., 154 ₂)when the optical path between the source of the beam (e.g., beam 125 ₃)and the primary PV cell (e.g., 154 ₃) assigned to that beam is fully orpartially blocked. After validating the signature and power of beam 125₃ at cell 154 ₂, transmitter is instructed via the wireless link toraise the power of the beam 125 ₂ to a higher value. Although the aboveembodiments of the present invention are described with reference tochanging the power of the laser beam from an eye-safe level to a higherpower level once the laser beam is validated, it is understood that inother embodiments, in place of using a variable-power laser source, twosources of laser may be used, one operating at an eye-safe level forsignaling and validation at the receiver, as described above, and onefor operating at a higher level for charging the device.

It is understood that, in accordance with the embodiments of the presentinvention, a laser beam may be redirected and identified as a valid beamat any PV cell so long as that beam does not intersect another beam asit is being redirected. For example, when the laser sources and the PVcells are laterally shifted in space so that either the laser sources,or the PV cells, or both are in different planes, the beams can beredirected to different PV cells with a much lower probability ofintersecting one another as they are redirected.

FIG. 6 is a simplified high-level block diagram of a wireless laserpower transfer system 500 with active safety protection, in accordancewith another exemplary embodiment of the present invention. System 500is similar to the embodiments shown in FIGS. 2-5 except that system 500is shown as including a multitude of transmitters having laser sourcesdisposed on different panels positioned at different locations within aclosed environment, such as a room, to charge a device 180. FIG. 6 showstwo such transmitters 110 and 210 having laser sources disposed onpanels 115 and 215, but it is understood that a wireless laser powertransfer system, in accordance with embodiments of the presentinvention, may have any number of transmitters dispersed throughout agiven space, with different transmitters having laser sources disposedon different panels having different locations and/or orientations withrespect to the PV cells.

Each of transmitters 110 and 220 is shown as including, in part, ksources of lasers each generating a beam directed toward a PV cell.Transmitter 110 is shown as including laser sources 120 ₁, 120 ₂ . . .120 _(k) adapted to generate laser beams 125 ₁, 125 ₂ . . . 125 _(k).Transmitter 210 is shown as including laser sources 220 ₁, 220 ₂ . . .220 _(k) adapted to generate laser beams 225 ₁, 225 ₂ . . . 225 _(k).Although not shown, it is understood that the embodiments of the presentinvention are not so limited and that in other embodiments, differenttransmitters may have different number of laser sources. Eachtransmitter is also shown as including, in part, a controller, and atransceiver. For example, transmitter 110 is shown as including acontroller 112 and a transceiver 116, and transmitter 210 is shown asincluding a controller 212 and a transceiver 216.

System 500 is also shown as including, in part, a receiver 150 havingdisposed therein a controller 152, a transceiver 156 and a multitude ofPV cells 154 _(j), wherein j is an integer. In the embodiment shown inFIG. 6, each laser beam is shown as striking a different one of the PVcells 154 _(j). It is understood, however, that the embodiments of thepresent invention are not so limited and that in other embodiments, oneor more of the laser beams may impinge on the same PV cell. As describedwith reference to other embodiments, each laser beam is modulated tohave a unique signature. A laser source 120 _(s) or 220 _(s), where s isan integer ranging from 1 to k in this exemplary embodiment, is enabledto switch from an off or an eye-safe state to a relatively high powerstate, as long as controller 152 validates the signature of the laserbeam it receives and determines that the path of the laser beam to thePV cell it is scanned to strike is unobstructed. Because in accordancewith the embodiment shown in FIG. 6, the laser sources are positioned ondifferent panels at different locations within, e.g., a room, if thepath of the laser beam from one of the laser source panels is blocked,the charging may be switched to or continue from another one of thelaser source panels. In some embodiments, controllers 112 and 212 areadapted to communicate and coordinate their actions via the wirelesslink established between their respective transceivers.

Although the above embodiments are shown as including a one-dimensionalarray of transmitters, it is understood, that in other embodiments, twoor three dimensional arrays of transmitters disposed in variouslocations may be used so as to increase the direct line-of-sight and thepower transmitted to the receiver. In one embodiment, to improveefficiency, an algorithm guides the scanning laser beams towards thereceive, while ensuring that no more than a single laser beamilluminates the same PV cell in the array of PV cells disposed in thereceiver. Such an algorithm further ensures that the laser beams do notinterest each other in space before arriving at the receiver.

In accordance with one aspect of the present invention, to furtherincrease safety and efficiency, the PV cells are coated with ananti-reflection coating. Such anti-reflection coating boosts theefficiency of the PV cell while minimizing the possibility ofundesirable reflections from the PV cell.

In accordance with yet another aspect of the present invention, thesurface of each PV cell is patterned. Such patterning may be random orspecifically designed to prevent reflections at a particular laserwavelength. Random patterns prevent direct mirror like reflections andproduce a diffused reflection from the surface that minimize the harmfuleffect of the laser beam on the human eye. In accordance with yetanother aspect of the present invention, the PV cells are formed usingGallium Nitride having bandgaps that accommodate laser wavelengths inthe range of 250 nm to 450 nm.

FIG. 7 is a flowchart of a process 300 for transmitting laser powerwirelessly, in accordance with one embodiment of the present invention.The laser power is set to an eye-safe level initially at 302 andscanned. The scanning continues at 304 until the laser beam is detectedat 306 by a PV cell. If the beam is detected as not having the expectedsignature at 308, the process moves to 304 at which point the scanningof laser beam is repeated. If the laser beam is detected as having theexpected signature at 308, and is further determined to have theexpected power level at 312, the laser power is caused to increase to ahigher value at 314. If the laser beam is detected as not having theexpected power level at 312, the process moves to 304 at which point thescanning of the laser beam is repeated.

FIG. 8 is a flowchart of a process 400 for controlling a laser sourcethat has been previously detected by a first PV cell as having theexpected power level and signature (validated) and is thus operating ata relatively high level to charge a device, in accordance with oneembodiment of the present invention. At 402, the laser beam power iscontinued to be monitored. If at 404 it is determined by the receiverthat the laser power is at or near the expected power level, the laserbeam is caused to continue to impinge of the PV cell. If at 404 it isdetermined by the receiver that the laser power is below the expectedlevel (e.g., due to obstruction of the laser beam path), the laser beamis shut off or reduced to an eye-safe level at 408. The laser power ismaintained at the off or eye-safe level for a predefined time period at410. Then to determine if the obstruction was caused by a moving objectthat is no longer obstructing the beam path, at 412, the laser beam isset to an eye-safe level if it was previously shut off at 408 and causedto strike the first PV cell again. If at 414 the first PV cell canvalidate the beam again, the beam is caused to continue to strike thefirst PV cell at 406. If, however, at 414 the first PV cell is unable tovalidate the beam (the path to the first PV cell remains obstructed),the beam is caused to scan at 416 for another PV cell that may beavailable and can validate the beam.

The above embodiments of the present invention are illustrative and notlimitative. The embodiments of the present invention are not limited bythe number of laser sources in each transmitter or the number oftransmitters. The above embodiments of the present invention are notlimited by the number of photo-voltaic cells. The above embodiments ofthe present invention are not limited by the modulation schemes used tomodulate the laser beams. The above embodiments of the present inventionare not limited by the wavelength of the laser sources. Othermodifications and variations will be apparent to those skilled in theart and are intended to fall within the scope of the appended claims.

What is claimed is:
 1. A wireless laser power transfer systemcomprising: a transmitter comprising: at least a first source of laserbeam; a first controller adapted to vary a power and a direction of thefirst laser beam, said first controller further adapted to modulate thefirst laser beam; and a first communication system; and a receivercomprising: at least a first photo-voltaic cell; a second controlleradapted to demodulate and detect the power of the modulated laser beamreceived from the first source of laser; and a second communicationsystem adapted to establish a wireless link with the first communicationsystem.
 2. The system of claim 1 wherein the transmitter comprises atleast a second source of laser beam, wherein said first controller isadapted to vary a power and a direction of the second laser beam, andwherein said first controller is further adapted to modulate the secondlaser beam.
 3. The system of claim 2 wherein said first controllermodulates the first and second laser beams using a same modulationtechnique.
 4. The system of claim 3 wherein said receiver furthercomprises a second photo-voltaic cell.
 5. The system of claim 4 whereinsaid first controller is further adapted to cause the second laser beamto strike the second photo-voltaic cell.
 6. The system of claim 1wherein said first controller is further adapted to cause the firstlaser source to operate at a first power level if the power of the laserbeam received at the receiver matches an expected power level.
 7. Thesystem of claim 6 wherein said first controller is further adapted tocause the first laser source to operate at a second power level if thepower of the laser beam received at the receiver does not match theexpected power level, said second power-level being either zero or aneye-safe power level.
 8. The system of claim 7 wherein said firstcontroller causes the first laser source to operate at the first orsecond power level in response to data the first controller receivesfrom the second controller, said data exchanged between the first andsecond communication systems.
 9. The system of claim 4 wherein saidfirst laser source is disposed on a first panel and said second lasersource is disposed on a second panel, said first and second panels beingpositioned at different orientations with respect to the firstphoto-volatile cell.
 10. The system of claim 1 wherein said laser has abandwidth ranging from 250 nm to 450 nm.
 11. A method of transferringlaser power wirelessly comprising: setting a power of at least a firstlaser beam to a first value; modulating the first laser beam; deliveringthe first laser beam to at least a first photo-voltaic cell;demodulating the delivered laser beam; detecting the power value of thedelivered laser beam; and varying the power of the first laser beam to asecond value greater than the first value if the detected power valuematches an expected power.
 12. The method of claim 11 furthercomprising: generating at least a second laser beam; modulating thesecond laser beam; and varying a power and a direction of the secondlaser beam.
 13. The method of claim 12 wherein said first and secondlaser beams are modulated using a same modulation technique.
 14. Themethod of claim 13 further comprising: disposing a second photo-voltaiccell adjacent said first photo-voltaic cell.
 15. The method of claim 14further comprising: causing the second laser beam to strike the secondphoto-voltaic cell.
 16. The method of claim 11 further comprising:changing the power of the first laser beam from the second value to thefirst value if the detected power value does not match the expectedpower value.
 17. The method of claim 16 further comprising: changing thepower of the first laser beam from the first value to the second valuefollowing the change from the second value to the first value if thepower value is detected to match the expected power value following anexpiration of a first time period.
 18. The system of claim 17 furthercomprising: causing the power of the first laser beam to change from thefirst value to the second value, and from the second value to the firstvalue in response to data exchanged wirelessly between a firstcontroller controlling the first laser beam and a second controllerresponsive to the first photo-voltaic cell.
 19. The method of claim 14wherein said first laser source is disposed on a first panel and saidsecond laser source is disposed on a second panel, said first and secondpanels being positioned at different orientations with respect to thefirst photo-volatile cell.
 20. The method of claim 1 wherein said laserbeam has a bandwidth ranging from 250 nm to 450 nm.
 21. The system ofclaim 1 wherein each of said first and second communication systems isselected from a group consisting of a transmitting unit, a receivingunit, and a transceiver.
 22. A wireless laser power transfer systemcomprising: a transmitter comprising: at least first and second sourcesof laser beams, said first laser operating at an eye-level safe leveland said second laser source operating at a level higher than theeye-safe level; a first controller adapted to vary a direction of thefirst and second laser beams, said first controller further adapted tomodulate the first laser beam; and a first communication system; and areceiver comprising: at least a first photo-voltaic cell; a secondcontroller adapted to validate the first laser beam received by thephoto-voltaic source; and a second communication system adapted to senda signal to the first communication system to cause the second laserbeam to strike the photo-voltaic cell after the validation of the firstlaser beam.